The use of stem cells in veterinary medicine such as equine medicine opens the way to a wide range of therapeutic opportunities by promoting an optimal regeneration of the injured tissue. Indeed, tendinitis and osteoarthritis are very frequent pathologies in equine medicine and unfortunately have a poor prognosis. In fact, musculoskeletal injuries are the most common source of injuries for competing horses. Although it is well known that (almost) adult tissues have some tissue-specific progenitor cells, these are often not sufficient for an efficient repair. Thus, effective regenerative medicine requires an exogenous input of cells in greater numbers than those that are present normally within the tissue. These cells should both be able to repair the lesion as well as to coordinate the healing process.
In current equine veterinary practice, the most commonly used stem cells are adult bone marrow-derived and adipose tissue-derived mesenchymal stem cells (MSCs), as well as Wharton's jelly MSCs (Schnabel et al., 2013, Iacono et al., 2012). Bone marrow aspirate is typically harvested from the sternum (marrow spaces 3-5) or ilium (Adams et al., 2012) and adipose tissue is generally harvested from the tail head region (Gutierrez-Nibeyro, 2011). Wharton's jelly is isolated from umblical cord (Iacono et al., 2012). These sampling methods are quite invasive, often not appreciated by owners of competing horses and can provoke some infections.
A second shortcoming for veterinary research is the lack in commercially available specific antibodies. For this, human antibodies need to be used, and their cross reactivity in animals such as horses needs to tested. As an example, only 4% of human antibodies react with equivalent equine proteins. Valid immunophenotyping further necessitates proper use of control isotypes to exclude non-specific antibody reactions and positive control cells to confirm cross reactivity in e.g. horses. There are hence no standard specifications or markers to ensure the quality of the animal or equine stem cells commercially available. Nevertheless, some research groups have tried to effectively characterize mesenchymal stem cells (MSCs) from various animal origins such as: bone marrow, adipose tissue, umbilical cord, umbilical cord blood, Wharton's jelly, peripheral blood and very recently periosteal tissue and muscle (Radtke et al., 2013). Radtke and co-workers in this respect reported on a process for the generation of equine muscle-derived mesenchymal stem cells (MSCs), wherein large muscular biopsies (6 g weight) are collected from horse cadavers. This method is hence highly invasive and not useful for living and competing horses. Secondly, the stem cells obtained are isolated from the biopsies by means of enzyme digestion techniques, which limit the possibilities. Third, the cells obtained by the process of Radtke and co-workers are positive for CD90 and CD44, but negative for CD45, CD34, CD146 and CD105. This negativity for CD105 was reported as being common in equine mesenchymal stem cells (MSCs) by Radtke et al., 2013.
From the above, it is clear that new methods are needed for producing mesenchymal stem cells (MSCs) from mammalians such as horses that involve a minimal invasive effort.